Thermodynamic Tuning of Au-Ag-Cu Nanoparticles with Phase Separation and Ordered Phase Formation

摘要

Metallic nanoparticles have been widely studied because of their unique and potentially useful optical properties, and they are expected to be applied to high-performance photocatalyst and sensing applications. In particular, nano- particles of noble metals, such as Au, Ag, and Cu, exhibit optical resonances based on surface plasmons, which can efficiently generate hot electrons. One strategy to fully tune the optical properties of these noble metal nanoparticles is to engineer the dielectric properties by alloying, which however is not trivial due to the existence of interphase and thermodynamic phase separation. In this study, we propose a new approach for designing and tuning the nanoparticles through thermodynamic processes. We fabricated Au-Ag-Cu ternary alloy nanoparticles through dewetting by thermally annealing thin films and investigated the optical properties and structures by transmission electron microscopy. The fabricated Au-Ag-Cu nanoparticles exhibited single or double plasmonic resonances depending on the elemental composition of samples, mainly determined by phase separation. The optical properties change accordingly, depending on element distribution and phase separation. This suggests that the nanoparticle function can be thermodynamically controlled by appropriately choosing the alloy composition and thermal processes.